Matchhead igniters and compositions and method for their manufacture



Aug. 7, 1962 D. T. ZEBREE 3,048,507 MATCHHEAD IGNITERS AND COMPOSITIONSAND METHOD FOR THEIR MANUFACTURE Filed Dec. 51, 1956 2 Sheets-Sheet 1FLASH QUALITIES OF MATCHHEADS WITH SNOW FLOSS DIAZODINITROPHENOL /KC I0/Mg./SNOW FLOSS /NITROCELLULOSE 26.0/47] HOS/2% FIG.| FIG. 2

FLASH QUALITIES OF MATCHHEADS WITHOUT SNOW FLO-SS DIAZODINTROPHENOL KCI0 Mg/ NITROCELLULOSE FIG. 4 FIG.5

DAVID T ZEBREE INVENTOR.

AGENT Aug. 7, 1962 D, T. ZEBREE 3,048,507

MATCHHEAD IGNITERS AND COMPOSITIONS AND METHOD FOR THEIR MANUFACTUREFiled Dec. 31, 1956 2 Sheets-Sheet 2 FIG? DAVID T ZEBREE INVENTOR.

BY W AGENT United States Patent MATCHHEAD XGNITERS AND COMPOSETIQNS AlQDMETHOD FDR THEIR MANUFACTURE David Thomas Zebree, Kingston, N.Y.,assignor to Hercules Powder Company, Wilmington, Del., a corporation ofDelaware Filed Dec. 31, 1956, Ser. No. 631,032 Claims. (Cl. 149-64) Thisinvention relates to new ignition compositions. In one aspect thisinvention relates to ignition compositions of the matchhead type,containing a siliceous material, for use in electric initiators. Inanother aspect this invention relates to matchheads exhibiting improvedregularity of flashing and improved sensitivity to ignition by virtue ofa siliceous material contained therein. In still another aspect thisinvention relates to a single dip method for making matchhead ignitersemploying a siliceous material in the dip solution to facilitate uniformpickup in the formation of matchheads of uniform size and strength onthe ignition element. In still another aspect this invention relates tothe utilization of siliceous materials as agents for facilitatingmanufacture of matchhead dipped bridges and as components which impartmarked improvement to the dipped bridge so produced.

Blasting cap charges comprise generally a base charge of a detonatingexplosive such as pentaerythritol tetranitrate, a heat-sensitive primercharge such as diazodinitrophenol superposed on the base charge and areadily ignitable ignition charge capable of firing the primer charge bythe flame generated. In the case of delay caps an additionalslow-burning composition or delay fuse is generally included between theignition and primer charges and exhibits such a predetermined rate ofburning that the specified time interval elapses between the applicationof the firing current and the explosion of the primer charge.

Matchhead igniter charges have been used in the art for some time. As iswell known, a matchhead-type igniter comprises a charge of a mixture ofa flash material, an oxygen supplier and a binder therefor in directfixed contact with an ignition element, generally a resistance or bridgewire and functions to produce a hot flame to initiate a suitableheat-sensitive material such as a primer in a blasting cap.

Matchhead igniters characteristically present field problems withreference to irregularity of flash, inconsistency in lighting the delayfuse and erratic sensitivity to ignition by the bridgewire and are forthat reason often undesirable as igniters in delay caps. Further,manufacture of matchhead-type igniters exhibiting constant uniformity ofstrength and size has always presented a problem.

This invention is concerned with new matchhead-type compositions whichhave overcome problems heretofore precluding their broader use asigniters in delay caps, and with a method by which they can bemanufactured to exhibit uniformity in size and strength.

An object of this invention is to provide new compositions of thematchhead type. Another object is to provide matchhead compositionsexhibiting improved characteristics making them especially suitable asigniters in delay blasting caps. Another object is to provide improvedmatchhead-type igniters. Another object is to provide -a method formanufacture of matchhead-type igniters exhibiting greater uniformity ofsize and strength than heretofore. Another object is to provide for theutilization of siliceous materials in the manufacture of matchhead-typeigniters and as a component of improved igniters so produced. Otheraspects and objects will be apparent from the accompanying disclosureand the appended claims.

In accordance with this invention is provided a bound mass of a solidheat-sensitive material capable of flash combustion upon being heated,in admixture with a solid material capable of supplying oxygen for saidcombustion and a suffioient amount of a siliceous material of the groupof natural occurring, and synthetic, silicas and silicates having aparticle size within the range of 0.02. to 4 microns, to impart improvedregularity to said flash. Also in accordance with this invention amethod is pro vided for the manufacture of a matchhead-type igniterwhich comprises contacting a heating element with a volatile organicliquid suspension of a heat-sensitive material and an oxygen supplier,as an igniter powder, together with an amount of a siliceous material ofthe group of natural occurring, and synthetic, silicas and silicateshaving a particle size within the range of 0.020 to 4 microns,sufficient to maintain said suspension, and a binder material in amountsufl'icient to bind the said suspended material as a solid mass whensaid solvent is evaporated therefrom; withdrawing said element from saidsuspension with suspended materials adhered thereto; and drying theresulting adhered material. Still in accordance with this invention amatchhead igniter in each of a plurality of electric delay blasting capsis fired while maintaining a siliceous material of the group of naturaloccurring, and synthetic, silicas and silicates having a particle sizein the range of 0.020 to 4 microns in each igniter, in an amountsufficient to impart improved regularity of flash thereto.

Exemplary of suitable composition components of this invention arep-phenylenediamine dipicrate, diazodinitrophenol, mercury fulminate,lead mono nitro resorcinate, lead styphnate and the like, asheat-sensitive materials; potassium chlorate, potassium perchlorate,potassiumnitrate, potassium permanganate, sodium nitrate, lead chromate,barium peromde, oxides of lead and the like, as oxidizers; nitrostarch,nitrocellulose and the like, as binders; and celite, kieselguhr,synthetic hydrated silicas, mica, complex natural silicates,diatomaceous materials, metal salts of silicic acid, synthetic silicasand the like, all finely divided to a particle size in the range of0.020 to 4 microns, as siliceous components.

A fuel element such as magnesium, aluminum, iron, chromium, lead, boron,sulfur and the like can be included in the suspension when desired tofacilitate combustion to produce additional heat during the flashcombustion.

Siliceous material components of the matchhead compositions of thisinvention provide for a marked reduction in irregularities in flashingand erratic sensitivity to ignition by the bridgewire. The siliceousmaterial also provide during the manufacturing process of this invention for a markedly improved uniformity in matchhead size and physicalstrength. These advantages will be more apparent in light of theaccompanying disclosure.

Celite, above referred to, is a soft earthy formation of siliceousskeletons of microscopic aquatic plants called diatoms. Snow Floss is atrade name given to such a material in a highly purifiedstate such as tobe substantially white. Snow Floss is a now preferred siliceouscomponent of the matchheads of this invention, and several embodimentsare therefore described in terms of Snow Floss. Of course, celite, in abrown and less purified form, and other siliceous materials, are alsohighly suitable as a siliceous material component of the matchheadcompositions of this invention. All such siliceous materials referred toherein are of particle size of from 0.020 to 4 microns.

In accordance with a specific embodiment of the method of manufacture ofthis invention, the matchhead composition ingredients including asiliceous material, preferably Snow Floss, are prepared as a suspensionin a suitable volatile organic solvent, and a bridgewire is 'ice thendipped into the suspension during which time materials in suspensionadhere to the bridgewire. The wire, with resulting adhered material, isthen withdrawn, and the adhered material is dried to form a drymatchhead composition strongly adhered to the wire. The proportions ofoxidizer, flash material, and binder are any such proportions known inthe art as suitable for formmga matchhead composition. The Snow Floss ispresent 1n an amount sufiicient to maintain the resulting suspension atleast for a time to enable representative proportions of the suspendedmaterials, including the Snow Floss to contact the bridgewire. Thepreferred suspension contains the ingredients in a concentration suchthat a significant settling of ingredient can occur only after there hasbeen time for a number of dips, i.e., for dipping a plurality ofelements. Thus the need for continuous stirring or agitation iseliminated, whereby the suspended materials are substantially static andadhere to the bridgewire in a matter of a few seconds. The suspensioninto which the bridgewire is dipped generally contains on a weight basisfrom about 11 to 65 percent heat-sensitive material, 15 to 70 percentoxygen-supplying salt, 2 to 48 percent siliceous material, and from 16to 55 percent binder solution. Appropriate amounts of extra fuel, e.g.,finely divided magnesium, are also included, when desired.

More specifically, a heat-sensitive material, say flash gradediazodinitrophenol, an oxidizer such as potassium perchlorate, and SnowFloss are admixed, in a suitable solvent, as butyl acetate, employingany suitable method such as ball milling. The wet milled mixture is thensized to say about 1 to 70 microns, the preferred range being in theorder of about 1 to 20 microns. The excess solvent in the mixture isremoved by decantation and the resulting admixture is then admixed witha suitable binder such as a 30 percent solution of nitrocellulose inethyl acetate in an amount to form the desired suspension. Due toevaporation, ethyl acetate is added periodically to maintain the desiredconsistency of the ingredients. A plasticizer can be used, if desired,in the binder solution to maintain desired flexibility during the dippedbridge manufacture. A bridgewire affixed to the terminal ends of a setof leg wires is then dipped or swept through the suspension to permitthe suspended ingredients to adhere to the bridge so that when thesolvent is initially evaporated from the adhered material, the residueis uniformly deposited on the wire. The adhered material is thencompletely dryed to permit evaporation of the remaining solvent andformation of the matchhead igniter. The size and uniformity of thematchhead composition is controlled by the manner in which the wire ispulled through the wet mixture and by the viscosity of the suspension.When employing nitrocellulose as a binder, and Snow Floss, the matchheadoften has a size say for example about 0.14 inch by 0.09 inch by 0.08inch. However, other sizes can be made, a larger size being for example0.15 inch by 0.12 inch by 0.10 inch. In some instances when forming arelatively large matchhead size, a second dip may be advantageouslyemployed.

Prior to dipping it is preferable that the terminal leg wires beassociated in the ignition plug to be inserted in the cap so that afterthe dipped bridge is formed, the plug, with terminal wires and dippedbridge, can be directly pressed into the cap. An air space is permittedbetween the plug and the top of the priming explosive or fuse as thecase may be. An exemplary air space has a length from about to /2 inch,a space in the order of about inch being often advantageously employed.

The dip method involves dipping the bridgewire into the ingredientsuspension to a predetermined depth and then allowing the matchheadmaterial to form completely around the bridgewire. Therefore, it isimportant that the composition of the suspension be maintained constantand that the depth of immersion of the bridge- Wire be withoutsubstantial variance and that the removal of the wire be at a uniformrate in a uniform direction. The faster the bridgewire is removed, thelarger the bead size.

In the matchhead composition the function of the heat-sensitive materialis to provide the flash, and the function of the oxidizer is to supplysufficient oxygen to support flash burning. In those instances wherein afuse in a delay assembly requires a large amount of heat for itsignition, a fuel such as magnesium, aluminum, or the like is included inthe matchhead for supplying such heat. The siliceous material componentregulates the burning speed of the matchhead mixture and accordinglycontrols the flashing qualities of the matchhead. When substantialquantities of the siliceous material are utilized, the flame produced bythe burning heat-sensitive powder is sustained for longer periods and asa result makes it possible to use little or no extra fuel.

I have found that without the siliceous component ingredient, the pickupfeatures of the matchhead mixture are not satisfactory. That is to say,without the presence of say Snow Floss, there is .a marked settling ofthe ingredients in the solution so that there is a nonuniformdistribution of the materials in the suspension which causes aninconsistency in matchhead product composition, i.e., from dip to dip.Furthermore, the siliceous component, by virtue of imparting improvedpickup features and distribution of ingredients in the suspensionprovides for a matchhead or bead of constant predetermined sizedependent upon the rate at which the assembly is withdrawn from thesuspension.

Nitrocellulose is advantageously employed in the suspension or lacquer,not only as an ultimate binder material, but it also facilitatessuspension of the composition ingredients and aids in control of theflash properties of the matchhead.

In the preparation of the suspension, about parts of the wet mixture ofingredients are mixed with about 30 parts of the lacquer, saynitrocellulose/butyl acetate, in about 20/80 Weight proportions.

The dipped bridge compositions, of the invention, by virtue of thepresence of the siliceous material component, exhibit markedly improvedregularity in flashing characteristics, as illustrated with reference tothe photos of FIGS. 1, 2, 3, 4, 5 and 6, showing a comparison inflashing qualities between a matchhead containing Snow Floss and withoutSnow Floss, i.e., containing no siliceous material. The photos show thegreat uniformity in flashing which is directly attributable to thesiliceous ingredient.

Instantaneous shots in delay caps are those which result from abnormalflash to transfer heat through the delay fuse to the primary explosivebefore there has been time for the delay fuse to burn. Such occurrencesare substantially eliminated in the practice of this invention in viewof the regularity of flash that is achieved. However, to further assureagainst any such occurrence, it is advantageous to maintain a suitableinterference between the shell and fuse, say in the order of from about0.001 to 0.005 inch.

With reference to FIG. 7 is further illustrated utilization of amatchhead composition of this invention as an igniter in a delayblasting cap. Referring to FIG. 7, metal shell 31 is flared at centralportion 32 to provide upper portion a having an inside diameter in theorder of about 0.259 inch and a lower portion b having a smaller insidediameter than portion a, namely in the order of about 0.0256 inch. Thelength of portion b is about inch; portion a will vary with the lengthof the shell as desired, usually between /2 and 6 inches. A suitablebase charge 34 such as pentaerythritol tetranitrate containing about 2percent graphite is placed in the bottom of shell 31 with priming charge36 such as straight diazodinitrophenol superposed on charge 34. Delayfuse 37 comprises a lead tube 0 containing a core "(1 of suitable delaypowder, as, for example, a barium peroxide/ selenium delay fuse and issuperposed on primer 36. Space 38 is disposed above fuse 37 into whichpin wires 39 extend. A dipped bridge 41 of this invention, connectingthe terminated ends of pin wires 39 in space 38, provides amatchhead-type igniter in accordance with the invention. Pins 39 extendupwardly from the bridge into upper portion a through semiconductiveplug 40, which can be an aluminum/candelilla wax composition, preferablyspaced from the shell wall, and then through a phenolic-type ignitionplug 44 superposed on the semiconducti've plug 40- and joined in anysuitable manner with leg wires 42 extending from the exterior into theupper portion a of the cap through the top sulfur seal 43 andwaterproofing material 46, the connection being preferably a solderjoint 45 the waterproofing plug. The bridgewire of dipped bridge 41 isadvantageously a plain or gold-plated nichrome wire on about 0.1 inchcenter and is say about 0.00175 inch in diameter.

A preferred matchhead composition of dipped bridge 41 is a milleddiazonitrophenol/potassium perchlorate/ Snow Floss/ nitrocellulose, inrelative weight proportions of 22./52.8/18.9/5.7.

The following data exemplify firing time obtained in a delay capdiscussed above employing a dipped bridge of this invention. Firing timedata, obtained when firing a loose lead-selenium ignition mixture, as acontrol, is included.

1 Control. Loose Pb-Se (0.7 gm) in stoichiometric proportions employedas the ignition mixture in lieu of a matchhead igniter.

In carrying out these shots the inside diameter of lower section b was0.254 inch, the upper section diameter being 0.259 inch, the length offlared cap (the taper) extending over about 17/32 inch of the shelllength, the shell being 2.5 inches long. The dipped bridge was a mixtureof flash grade diazodinitrophenol/potassium perchlorate/ Snow Floss ballmilled in respective 24/56/20 ratios. The ball milling was done in 2.4percent nitrostarch97.6 percent butyl acetate solution for 4 hours. Theexcess butyl acetate was siphoned subsequent to settling for about 12hours. The resulting wet mixture was then blended with a solution ofnitrocellulose in ethyl acetate in a respective weight ratio of 100/ 30.On a dry basis the milled mixture contained diazodinitrophenol/potassium perchlorate/ Snow 'Floss/ and lacquer in relative weightproportions of 22.6/52.8/18.9/5.6. The

BaO /Se(7525 /PbSn was respectfully 80/20 standard fuse powder, the PbSnbeing about 85/ 15. An air space between the top of the delay fuse andthe face of the semiconductive plug was inch. The distance between thetop of the fuse and the bottom of the dip bridge was inch.

The dipped bridge compositions of this invention by the presence of asiliceous material as exemplified by Snow Floss exhibit markedlyimproved voltage breakdown characteristics. Thus in one series of teststhe composition of the dipped bridge material wasdiazodinitrophenol/potassium perchlorate/Snow Floss/and nitrocellulosein respective weight ratios of 22.6/52.8/ 18.9/ 5.7 except that the SnowFloss was omitted from one composition. In determination of breakdownvoltage based on 25 shots for each composition, the lowest breakdownvoltage encountered in the presence of Snow Floss was 3000 volts,

6 whereas in the absence of Snow Floss the lowest value was 1100 volts.

Other tests have shown the advantages of the dipped bridge compositionof this invention to series firing. Thus 5 a composition of flashdiazodinitrophenol/potassium perchlorate, 24/56 was found to have acirtical firing current of 1 amp. The same composition, except that itcontains about 19 percent Snow Ross, is characterized by a criticalfiring current of 0.8 amp. These results were obtained "by firing 30caps in series, each at 110 volts and measuring the minimum currentrequired for firing.

Although a proportion of siliceous material in the matchhead in a rangeof say 3 to 55 percent can be employed, I prefer generally to employ aproportion in the range of say from 10 to 25 weight percent, 18 to 20percent being optimum in many instances. This latter range (18 to 20percent) particularly as applied to Snow Floss, gives especially smoothflashing and generally the most desirable electric firing properties.

The amount of extra fuel component, when employed, depends upon thespecific heat requirements. Generally, however, from about 5 to 40weight percent of extra fuel is suflicient. In utilizing a metal, asextra fuel, having an atomic weight below about that of iron, from about5 to weight percent is generally sufficient, heavier metals being mostadvantageously employed within a range of about 10 to weight percent.

The following tabulation sets forth preferred ranges Auxiliary flashcompositions, not sensitive to an ignition wire, can be employed whendesired in form of loose powder mixture intermediate the matchhead anddelay fuse, when the fuse powder is somewhat more difficult than usualto light. Exemplary auxiliary compositions are bariumperoxide-tellurium, barium peroxideselenium and other gasless mixtures.

As will be evident to those skilled in the art, various modificationscan be made or followed, in the light of the foregoing disclosure anddiscussion, without departing from the spirit or scope of the disclosureor from the scope of the claims.

55 What I claim and desire to protect by Letters Patent .1. In anelectric blasting cap assembly containing a bound ignition mixture, as amatchhead, around the bridgewire, the improvement comprising, on aweight basis, as said matchhead, from 9-70 percent of a primaryinitiating explosive capable of flash combustion in response to heatdeveloped by passage of electric current through said bridgewire, from10-75 percent of an inorganic solid oxidizer capable of decomposition toliberate free oxygen for support of said flash combustion in response tosaid heat developed as above described, from 1.5-15 percent of a bindermaterial and from 3-55 percent of a siliceous material selected from thegroup consisting of natural occurring, and synthetic, silicas andsilicates, having a particle size within the range of 0020-4 microns.

2. A blasting cap assembly of claim 1 wherein said siliceous material isa diatomaceous earth.

3. A blasting cap assembly of claim 2 wherein said diatomaceous earthcomprises siliceous skeletons of microscopic aquatic plants and is ofsufliciently purified state as to be substantially white.

4. A blasting cap assembly of claim 3 wherein said primary initiatingexplosive is at least one of the group consisting of diazodinitrophenoland phenylenediamine dipicrate, and wherein said oxidizer is at leastone of the group consisting of potassium chlorate and potassiumperchlorate.

5. An assembly of claim 2 containing from 10-25 percent of saiddiatomaceous earth.

6. An assembly of claim 3 containing from 18-20 percent of saidsiliceous skeletons.

7. In an electric blasting cap assembly containing a bridgewire, amatchhead around the said bridgewire and lead wires from said bridgewireto the outside of said cap, a detonatable base charge spaced from saidmatchhead, a primer charge intermediate said detonatable charge and saidmatchhead and a delay fuse intermediate said primer and said matchhead,the said matchhead being ignitable in response to heat developed bypassage of electric current through said bridgewire via said lead wires,the said delay fuse being ignitable by heat from ignition of saidmatchhead and, when burned, being in operative relation with said primerto cause detonation of said primer, and the said detonatable chargebeing detonatable in response to detonation of said primer, theimprovement comprising as said matchhead, on a weight basis, from 9-70percent of a primary initiating explosive capable of flash combustion inresponse to heat developed by passage of electric current through saidbridgewire, from 10-75 percent of a solid inorganic oxidizer capable ofdecomposition to liberate free oxygen for support of said flashcombustion in response to said heat developed as above described, from1.5 to 15 percent of a binder material and from 3-55 percent of asiliceous material selected from the group consisting of naturaloccurring, and synthetic, silicas and silicates, having a particle sizewithin the range of 0.020-4 microns.

8. An assembly of claim 7 wherein said siliceous material is adiatomaceous earth.

9. An assembly of claim 8 wherein said diatomaceous earth comprisessiliceous skeletons of microscopic aquatic plants and is of suflicientlypurified state as to be substantially white.

10. An assembly of claim 7 wherein said primary explosive is at leastone of the group consisting of diazodinitrophenol and phenylenediaminedipicrate, and wherein said oxidizer is at least one of the groupconsisting of potassium chlorate and potassium perchlorate.

11. An assembly of claim 7 wherein said binder material is selected fromthe group consisting of nitrocellulose and nitrostarch.

12. An assembly of claim 7 wherein said matchhead contains from 9-55percent of said primary explosive, from 15-65 percent of said oxidizer,and from '5-55 percent of said siliceous material.

.13. In an assembly of claim 7, a supplemental ignition mixtureintermediate said matchhead and said fuse and ignitable by heatdeveloped from combustion of said primary explosive to thereby supplyadditional heat for ignition of said fuse.

14. A blasting cap assembly of claim 7 wherein said matchhead alsocontains from 5-40 weight percent of a fuel material selected from thegroup consisting of magnesium, aluminum, iron, chromium, lead, boron,and sulphur, the said material being combustible in response to saidflash combustion of said primary explosive so as to thereby provideadditional heat for ignition of said fuse.

15. In an assembly of claim 14, magnesium as said fuel.

References Cited in the file of this patent UNITED STATES PATENTS1,240,549 Du Pont Sept. 18, 1917 1,852,054 Kaiser Apr. 5, 1932 1,916,078Schless June 27, 1933 2,175,249 Burrows et al Oct. 10, 1939 2,287,093Ellis June 23, 1942 2,440,579 Frazer et al. Apr. 27, 1948 2,473,405Zebree June '14, 1949 2,478,501 Patterson Aug. 9, .1949 2,607,672 Spaethet al Aug. 19, 1952

1. IN AN ELECTRIC BLASTING CAP ASSEMBLY CONTAINING A BOUND IGNITIONMIXTURE, AS A MATCHHEAD, AROUND THE BRIDGEWIRE, THE IMPROVEMENTCOMPRISING, ON A WEIGHT BASIS, AS SAID MATCHHEAD, FROM 9-70 PERCENT OF APRIMARY INITIATING EXPLOSIVE CAPABLE OF FLASH COMBUSTION IN RESPONSE TOHEAT DEVELOPED BY PASSAGE OF ELECTRIC CURRENT THROUGH SAID BRIDGEWIRE,FROM 10-75 PERCENT OF AN INORGANIC SOLID OXIDIZER CAPABLE OFDECOMPOSITION TO LIBERATE FREE OXYGEN FOR SUPPORT OF SAID FLASHCOMBUSTION IN RESPONSE TO SAID HEAT DEVELOPED AS ABOVE DESCRIBED, FROM1.5-15 PERCENT OF A BINDER MATERIAL AND FROM 3-55 PERCENT OF A SILICEOUSMATERIAL SELECTED FROM THE GROUP CONSISTING OF NATURAL OCCURING, ANDSYNTHETIC, SILICAS AND SILICATES, HAVING A PARTICLE SIZE WITHIN THERANGE OF 0.020-4 MICRONS.